Photovoltage probe

Abstract

A photovoltage probe includes an optical modulator 1, an input / output optical fiber 2 connected to the optical modulator 1, two contact terminal mounting portions 5 and 6, and a package 8 housing a portion of the optical modulator 1 and the input / output optical fiber 2. The optical modulator 1 has two modulation electrodes 11 and 12, and outputs intensity-modulated incident light based on the voltage between the modulation electrodes. The two contact terminal mounting portions 5 and 6 have structures that connect contact terminals 3 and 4 that can contact the point to be measured, and are respectively connected to the modulation electrodes 11 and 12. The voltage signal induced between the contact terminals 3 and 4 is converted into a light intensity modulation signal and output. The package 8 has an electromagnetic shielding effect such that when the contact terminal mounting portions 5 and 6 are opened and electromagnetic waves of the measurement frequency are irradiated, the output signal intensity is attenuated by more than 15 dB compared to when the package is not present.

Description

Technical Field

[0001] The present invention relates to an optical voltage probe that converts a voltage signal obtained from a contact terminal into an optical modulation signal by applying it to an optical modulator, and outputs the optical modulation signal through an optical fiber. Background Technology

[0002] In recent years, various control devices employing high-speed CPUs and other technologies have been developed. As a countermeasure to prevent malfunctions, noise signals generated by the circuit boards and other components are detected, and noise tolerance tests are performed on the circuit boards. These tests require accurate measurement of the input and output signals of electrical components mounted on the circuit board and the electrical signals conducted along the wiring.

[0003] The general method for measuring electrical signals in electrical components or wiring is as follows: the electrical signal from the point to be measured is fed into a measuring instrument such as an oscilloscope using an electrical probe with contact terminals, and the conducted voltage waveform is measured. However, when the ground plane of the point to be measured is different from that of the measuring instrument, or when measuring the voltage signal between two ungrounded points, it is difficult to accurately measure the voltage waveform due to the interference of signals from the ground wire or the influence of the capacitance of the electrical probe. This influence of grounding or capacitance is particularly significant in the high-frequency field. Furthermore, in integrated circuits such as ICs and LSIs, the input and output impedances are often not 50Ω; for example, amplifier components have high-impedance inputs and low-impedance outputs. Therefore, if an electrical probe with a low input impedance is used to measure the noise input voltage, a current will flow into the probe side, causing the noise voltage that should be measured to decrease.

[0004] As a solution to this problem, a measuring instrument using a photovoltage probe was developed. The photovoltage probe converts a voltage signal into an optical signal, which is then transmitted to the measuring instrument via an optical fiber. In this method, because all the capacitance components of the probe are very small, the input impedance is very high, and the measured point is completely electrically isolated from the measuring instrument. The photovoltage probe can measure high-frequency components and prevents grounding interference or the introduction of electrical signal noise.

[0005] Examples of such measuring devices are described in Patent Documents 1 and 2. Patent Document 1 describes a photovoltage probe employing a capacitive optical modulator. Specifically, its structure involves applying a voltage signal at a contact terminal between two electrodes of a crystal with an electro-optic effect sandwiched between them. This causes the incident light transmitted from the optical fiber to be reflected within the crystal, resulting in a change in the polarization state of the light. This changed component is then transmitted via an optical fiber to an O / E converter as intensity modulation light by a photon detector. Patent Document 2 describes a photovoltage probe employing a waveguide-type optical modulator. A voltage signal at a contact terminal is applied between two modulation electrodes of a branch interference type optical modulator formed on a lithium niobate crystal substrate to obtain an intensity modulation signal. A device equipped with a light source and an O / E converter is connected to the photovoltage probe via an optical fiber.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 63-196863

[0009] Patent Document 2: Japanese Patent Application Publication No. 8-35998 Summary of the Invention

[0010] The technical problem that the invention aims to solve

[0011] As mentioned above, existing photovoltage probes can eliminate the grounding effects of electrical probes and prevent electrical signal noise from entering the wiring of the measuring device. However, existing photovoltage probes cannot eliminate the influence of electromagnetic wave noise propagating in the space around the photovoltage probe and directly reaching the modulation electrode. This is because, typically, the modulation electrode of an optical modulator, as mentioned above, has a high input impedance, and the wiring from the contact terminal to the modulation electrode acts as an antenna for receiving radio waves.

[0012] The purpose of this invention is to provide a photovoltage probe that can solve the above-mentioned problems and accurately measure the voltage signal of the measured point without being affected by surrounding electromagnetic noise.

[0013] Technical means to solve the problem

[0014] To solve the above problems, according to the first concept, the optical voltage probe according to the present invention includes an optical modulator, an input optical fiber and an output optical fiber connected to the optical modulator, two contact terminals or a two contact terminal mounting portion, and a package housing the optical modulator, the input optical fiber, and a portion of the output optical fiber; the optical modulator has at least two modulation electrodes, and outputs intensity modulation of incident light based on the voltage between the two modulation electrodes; the two contact terminals are connected to the modulation electrodes and can contact the point to be measured; the two contact terminal mounting portion has a structure that can connect the contact terminals that can contact the point to be measured, and is connected to the modulation electrodes; the voltage signal induced between the two modulation electrodes by the contact terminals is converted into an optical intensity modulation signal by the optical modulator and output from the output optical fiber; the package is characterized in that it has the following electromagnetic shielding effect: when the contact terminals or the contact terminal mounting portion are opened and electromagnetic waves of the measurement frequency are irradiated, the output signal intensity is attenuated by more than 15 dB compared to when the package is not present.

[0015] According to the photovoltage probe of the present invention, as described above, by covering the optical modulator with a package having an electromagnetic wave shielding effect, electromagnetic noise around the measurement location can be prevented from being received by the modulation electrode of the optical modulator or by wiring along the path to the modulation electrode. Although the photovoltage probe performs measurement by contacting the contact terminals with the measurement point such as the circuit board, the contact terminals can also be integrally provided with the photovoltage probe, or the contact terminals can be selected according to the purpose. Therefore, the photovoltage probe can also have a contact terminal mounting portion. As long as the package has an electromagnetic wave shielding effect that attenuates the received electromagnetic noise signal when the package is not connected (attenuating by more than 15 dB) in a state where the contact terminals are not connected, the photovoltage probe can achieve sufficient performance to realize the purpose of the present invention in practical applications. This is a fact confirmed by the inventors through experiments.

[0016] In this invention, metal is a representative material for the encapsulation used to achieve radio wave shielding, but in addition to metal, conductive materials such as carbon can also be used, and radio wave absorbers can also be used to construct the encapsulation. The shape of the encapsulation can be arbitrary, as long as it can house and cover the optical modulator and the wiring from the contact terminals to the modulation electrode inside. Furthermore, if it can be determined that the electrode or wiring functions as a radio wave receiving antenna, the encapsulation structure can also be a structure that only covers that part with metal, conductor, or radio wave absorber.

[0017] According to the second concept, the present invention, based on the photovoltage probe of the first concept, is characterized in that the encapsulation has a structure in which the interior is covered by a metal body. According to the invention of this concept, the most common and easily processed metal body is used as the encapsulation material. The encapsulation can be constructed by metalworking a metal plate, etc. Besides this method, another method can be used: the encapsulation is constructed using insulating resin or ceramic, etc., and a metal film is provided to cover its entire outer or inner surface. The encapsulation can also be constructed using a plate-like material with an internal metal layer. Furthermore, the metal body can also be a mesh-like metal body with a mesh size sufficiently small relative to the wavelength of the electromagnetic wave being shielded.

[0018] According to the third concept, the present invention, based on the photovoltage probe of the second concept described above, is characterized in that the encapsulation includes a layered or sheet-like metal body. According to this invention, the encapsulation can be constructed primarily of materials such as resin or ceramic, providing the necessary strength, and a metal film can be provided to cover its outer or inner surfaces. The surface of the encapsulation can be vapor-deposited with a metal film, bonded with metal adhesive tape, coated with a metal plating or metal material, and so on. A combination of materials with excellent manufacturing cost and lightweight properties can be selected and used with the metal film.

[0019] According to the fourth concept, the present invention, based on the photovoltage probe of the first to third concepts described above, is characterized by having the aforementioned contact terminal mounting portion, which is located inside the surface of the package. In the photovoltage probe, to prevent the reception of electromagnetic noise originating from the contact terminal during measurement, the length of the contact terminal is preferably as short as possible. When the contact terminal mounting portion is provided, if this portion protrudes outward from the package, the overall length of the protruding portion connected to the contact terminal also becomes longer, essentially becoming an antenna for electromagnetic noise. Therefore, according to the invention of this concept, the foremost end of the contact terminal mounting portion is located inside the surface of the package.

[0020] According to the fifth concept, the present invention, based on the photovoltage probe of the first to fourth concepts described above, is characterized in that the package has an electromagnetic wave absorber on its surface or inside to reduce the reflection of electromagnetic waves caused by the package. In the photovoltage probe according to the present invention, although the package with electromagnetic wave shielding effect can prevent direct detection of surrounding electromagnetic noise through modulation electrodes, electromagnetic noise is reflected due to the package being positioned close to the circuit board or other components being measured. When this noise is emitted by a portion of the circuit board or other components that functions as a receiving antenna, the signal measured from the contact terminals may be mixed with signals based on electromagnetic noise. According to the present invention, by providing an electromagnetic wave absorber in the package, electromagnetic noise can be absorbed, reducing electromagnetic noise reflection. Therefore, reflected waves of electromagnetic noise originating from the package positioned close to the measurement point can be reduced, further preventing the measurement from being affected by electromagnetic noise.

[0021] It should be noted that while it is preferable for the electromagnetic wave absorber to be located on the surface of the package, it can also be located inside the package, as long as it is located further outward than the metal body intended to provide electromagnetic wave shielding. The electromagnetic wave absorber used in this invention can be anything that reduces electromagnetic wave reflection. For example, materials such as: conductive electromagnetic wave absorbing materials made of conductive fiber fabrics that absorb current generated by electromagnetic waves through internal material resistance; inductive electromagnetic wave absorbing materials that increase surface inductive loss by mixing carbon powder or similar materials with dielectrics such as rubber, polyurethane foam, and polystyrene foam; and magnetic electromagnetic wave absorbing materials that absorb electromagnetic waves through magnetic loss, such as iron, nickel, and pure iron; and so on. Furthermore, the material shape can be a sheet material, a coated material, etc.

[0022] According to the sixth concept, the present invention, based on the photovoltage probe of the fifth concept, is characterized in that the package has a thin sheet of electromagnetic wave absorber on its surface. During the manufacturing of the package, according to the invention of this concept, as a final step, the electromagnetic wave absorber sheet can be adhered to the surface, thus simplifying the manufacturing process.

[0023] According to the seventh concept, the present invention, based on the photovoltage probe of the first concept described above, is characterized in that the package, by providing an electromagnetic wave absorber, achieves the aforementioned electromagnetic wave shielding effect and reduces the reflection of electromagnetic waves caused by the package. As described above, although conductive electromagnetic wave absorbing materials, inductive electromagnetic wave absorbing materials, and magnetic electromagnetic wave absorbing materials can be used as electromagnetic wave absorbers, the selection of their materials or composition, thickness, etc., can often achieve a sufficient electromagnetic wave shielding effect as shown in the first concept, in addition to obtaining the electromagnetic wave absorption effect. In this case, it is not necessary to additionally provide a shielding unit composed of a metal body or the like.

[0024] According to the eighth concept, the present invention, based on the photovoltage probe of the first to seventh concepts described above, is characterized in that the interval between the two contact terminals or the interval between the mounting portions of the two contact terminals is 3 mm or more. As mentioned above, one of the advantages of the photovoltage probe is its very high input impedance, thus reducing the electrical influence on the measurement point when the contact terminals are in contact with it, making accurate voltage signal measurement possible. To further enhance this advantage, the present invention further increases the input impedance by setting the interval between the contact terminals or the mounting portions of the contact terminals to 3 mm or more. Thus, by setting the interval to 3 mm or more, the influence of input impedance is eliminated during measurement, a fact confirmed by the inventors through experiments.

[0025] According to the ninth concept, the present invention, based on the first to eighth concepts of the photovoltage probe, is characterized in that the optical modulator is a branch-interference type optical modulator using an optical waveguide formed on a lithium niobate crystal substrate. The invention employs a branch-interference type optical modulator based on a conventionally used optical waveguide formed on a lithium niobate crystal substrate. The basic structure of the branch-interference type optical modulator consists of an input optical waveguide extending from the light incident side, two phase-shifted waveguides branching from the input waveguide, an output optical waveguide where the two phase-shifted waveguides converge and connect to the light emitting side, and modulation electrodes arranged side-by-side in the phase-shifted waveguides. Since the modulation electrodes apply a voltage signal to the phase-shifted waveguides, changing the refractive index of the phase-shifted waveguides, the light passing through the two phase-shifted waveguides converges and interferes with each other, thus modulating the light intensity. Because a small, efficient, and broadband optical modulator can be obtained, it is suitable for the photovoltage probe of the present invention.

[0026] According to the tenth concept, the present invention, based on the optical voltage probe of the ninth concept, is characterized in that the optical modulator is a reflective optical modulator that internally reflects and folds back the incident light, and the input optical fiber and output optical fiber are composed of a single input and output optical fiber. The reflective optical modulator of this invention employs a structure that reflects the incident light back to the incident side optical waveguide after reflection in a phase-shifted waveguide. By adopting this reflective optical modulator structure, compared to a transmission optical modulator, it can transmit twice the length of light with the same electrode length, thus achieving high efficiency, wide bandwidth, and miniaturization of the optical modulator. Furthermore, since the optical modulator is connected to a single optical fiber, it is easy to handle.

[0027] According to the eleventh concept, the present invention, based on the ninth or tenth concept of the photovoltage probe, is characterized in that at least one electrode between the two modulation electrodes is capacitively coupled to the two modulation electrodes. This invention employs a so-called segmented electrode, composed of multiple electrodes divided along its length and capacitively coupled to each other, as the modulation electrode. Generally, increasing the length of the modulation electrode along the optical waveguide increases the modulation efficiency and the detection voltage sensitivity of the photovoltage probe. However, increasing the length of the modulation electrode increases the capacitance. A large electrode capacitance leads to a higher electrical signal frequency, a decrease in equivalent impedance, and a reduction in the voltage applied to the electrode, thus reducing the modulation efficiency. Therefore, to detect high-frequency signals, it is preferable to minimize the electrode capacitance. A powerful means to improve this trade-off between the length and capacitance of the modulation electrode is to divide a single modulation electrode into multiple capacitively coupled electrodes. By using such a segmented electrode, a high-efficiency, broadband optical modulator can be obtained.

[0028] The effects of the invention

[0029] As described above, according to the present invention, a photovoltage probe can be obtained that can accurately measure the voltage signal of the measured point without being affected by surrounding electromagnetic noise. Attached Figure Description

[0030] Figure 1 This is a schematic structural diagram representing the photovoltage probe structure according to Embodiment 1, wherein... Figure 1 (a) is a top view with perspective. Figure 1 (b) is a perspective side view. Figure 1 (c) is a partially enlarged sectional view of the contact terminal mounting section.

[0031] Figure 2 This is a block diagram of a measurement system using a photovoltage probe according to Example 1.

[0032] Figure 3 This is a schematic diagram of one example of the reflective optical modulator structure built into the photovoltage probe of Embodiment 1, wherein... Figure 3(a) is a top view. Figure 3 (b) is the AA sectional view.

[0033] Figure 4 This is a schematic diagram of one example of the electromagnetic shielding effect measurement results of the package of the photovoltage probe in Example 1.

[0034] Figure 5 This is a schematic diagram of the photovoltage probe structure according to Embodiment 2, wherein... Figure 5 (a) is a top view with perspective. Figure 5 (b) is a partially enlarged sectional view showing the cross-sectional structure of the package.

[0035] Figure 6 This is a schematic diagram of the photovoltage probe structure according to Embodiment 3, wherein... Figure 6 (a) is a top view with perspective. Figure 6 (b) is a partially enlarged sectional view showing the cross-sectional structure of the package.

[0036] Figure 7 This is a schematic representation of the photovoltage probe structure according to Embodiment 4, shown as a transmittance top view.

[0037] Figure Labels

[0038] 1: Optical modulator; 2: Input / output optical fiber; 3, 4: Contact terminals; 5, 6: Contact terminal mounting parts; 7: Hoop; 8, 31, 51, 61: Encapsulation components; 9: Base; 10, 30, 50, 60: Optical voltage probes; 11, 12: Modulation electrodes; 13: Fixing components; 14: Insulator; 15: Terminal insertion part; 16: Wire; 17: Incident light; 18: Optical intensity modulation signal; 19: Electrical components; 21: Optical signal receiving and transmitting unit; 22: Light source; 23: O / E converter; 24: Receiving and transmitting splitter; 25: Amplifier 26: Output terminal; 27: Measuring device; 28: Input terminal; 29: Circuit board; 32: Metal package; 33, 54: Radio wave absorber; 35, 36: Measured value; 41: Substrate; 42: Branch interference type optical waveguide; 42a: Input and output optical waveguide; 42b, 42c: Phase shift optical waveguide; 43: Buffer layer; 44: Modulation electrode section; 45: Light reflection section; 46, 47, 48: Electrodes; 46a, 47a, 47b, 48b: Electrode section; 52: Resin package; 53: Metal sheet. Detailed Implementation

[0039] The photovoltage probe of the present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the same reference numerals are assigned to the same elements in the description of the drawings, and repeated descriptions are omitted.

[0040] Example 1

[0041] Figure 1 This is a schematic structural diagram representing the photovoltage probe structure according to Embodiment 1, wherein... Figure 1 (a) is a top view with perspective. Figure 1 (b) is a perspective side view. Figure 1 (c) is a partially enlarged sectional view of the contact terminal mounting section.

[0042] Figure 1 In this embodiment, the photovoltage probe 10 includes a photoelectric modulator 1, an input optical fiber connected to the photoelectric modulator 1, and an output optical fiber. The photoelectric modulator 1 has two modulation electrodes 11 and 12, and outputs light by intensity modulation of the incident light based on the voltage between the modulation electrodes 11 and 12. It also includes contact terminal mounting parts 5 and 6; the contact terminal mounting parts 5 and 6 have structures that can be connected to two contact terminals 3 and 4 respectively, which have structures that can contact the measurement point, and are respectively connected to the modulation electrodes 11 and 12. In this embodiment, the photoelectric modulator 1 is a reflective photoelectric modulator that internally reflects the incident light to refract it back. The optical fiber input to the photoelectric modulator 1 and the optical fiber output from the photoelectric modulator 1 are composed of one input-output optical fiber 2. The leading end of the input-output optical fiber 2 is fixed by being inserted into a sleeve 7 to attach and fix the incident and output end faces of the photoelectric modulator 1 to each other.

[0043] Furthermore, the optical modulator 1 and a portion of the input / output optical fibers 2 are housed within a cubic package 8 made of metal. The optical modulator 1 is fixed to a base 9 fixed within the package 8, and the input / output optical fibers 2 are fixed to the package 8 by rubber ring-shaped fixing components 13.

[0044] Contact terminal mounting parts 5 and 6, such as Figure 1 As shown in (c), the device consists of a cylindrical insulator 14 and a cylindrical terminal insertion portion 15 containing and fixed metal inside it. During measurement, contact terminal 3 is inserted into the terminal insertion portion 15 of contact terminal mounting portion 5, and contact terminal 4 is inserted into the terminal insertion portion 15 of contact terminal mounting portion 6. The terminal insertion portion 15 is fitted with a wire 16 for connecting the modulation electrode 11 or 12, and the insulator 14 is fixed to the package 8. In this embodiment, contact terminal mounting portions 5 and 6 are located further inward than the surface of the package 8. Furthermore, the center-to-center distance between the two contact terminal mounting portions 5 and 6 is approximately 5 mm, and the distance P between the two contact terminals 3 and 4 after installation is also approximately 5 mm. Thus, by increasing the contact terminal spacing by more than 3 mm, a high input impedance can be obtained.

[0045] Next, the measurement system using the photovoltage probe 10 of this embodiment will be described. Figure 2 This is a block diagram of a measurement system using a photovoltage probe according to Embodiment 1. (See diagram for example.) Figure 2As shown, incident light 17 is transmitted from optical signal receiving and transmitting unit 21 to optical voltage probe 10 via input / output optical fiber 2. Optical intensity modulation signal 18 output from optical modulator 1 is input to signal receiving and transmitting unit 21 via the same input / output optical fiber 2. Optical signal receiving and transmitting unit 21 includes a light source 22 such as a semiconductor laser, an O / E converter 23, a receiving and transmitting splitter 24 for separating incident light 17 from optical intensity modulation signal 18, and an amplifier 25. Outgoing light from light source 22 is coupled to input / output optical fiber 2 via receiving and transmitting splitter 24, and optical intensity modulation signal 18 returning from input / output optical fiber 2 is input to O / E converter 23 via receiving and transmitting splitter 24. In O / E converter 23, optical intensity modulation signal 18 is converted into an electrical signal, amplified by amplifier 25, and output to output terminal 26. This electrical signal is input to input terminal 28 of measuring instrument 27 such as oscilloscope. Receiving and transmitting splitter 24 can be constructed using any one of an optical circulator, optical fiber splitter, or semi-transparent mirror.

[0046] Figure 2 This describes the voltage signal applied between two terminals of an electrical component 19 assembled on a circuit board 29, which is used as the measurement point. The contact terminals 3 and 4 of the photovoltage probe 10 are brought into contact with the two terminals of the electrical component 19 that are to be measured.

[0047] As described above, the voltage signal input through contact terminals 3 and 4 is guided to modulation electrodes 11 and 12, and the voltage signal is converted into a light intensity modulation signal 18 by the light modulator 1. The light intensity modulation signal 18 is converted into an electrical signal in the light signal receiving and transmitting unit 21. By observing its voltage waveform with measuring instrument 27, the waveform of the voltage signal applied between the two terminals of the electrical component 19 can be determined.

[0048] Figure 3 This is a schematic diagram illustrating one example of the structure of the reflective optical modulator 1 built into the photovoltage probe 10 in this embodiment, wherein... Figure 3 (a) is a top view. Figure 3 (b) is the AA sectional view.

[0049] according to Figure 3 The optical modulator 1 comprises a substrate 41 cut from a lithium niobate (LiNbO3) crystal with an electro-optic effect using an X-cutting machine, a branched interference-type optical waveguide 42 formed by Ti diffusion on the upper side of the substrate 41, a buffer layer 43 formed on the upper side of the substrate 41, a modulation electrode portion 44 containing modulation electrodes 11 and 12 formed on the buffer layer 43, and a light-reflecting portion 45 disposed at one end of the substrate 41. The modulation electrode portion 44 is a two-layer film of chromium (Cr) and gold (Au) formed by sputtering or the like.

[0050] The branch-interference type optical waveguide 42 consists of one input / output optical waveguide 42a extending on the incident side of the input light, and two phase-shifted waveguides 42b and 42c extending from the input / output optical waveguide 42a branching into two. The width W of the input / output optical waveguide 42a or the phase-shifted optical waveguides 42b and 42c is equal in the direction perpendicular to the extension direction. Furthermore, the lengths of the phase-shifted optical waveguides 42b and 42c are substantially equal in the extension direction.

[0051] The width W of these optical waveguides ranges from 5 to 12 μm. The length of the phase-shifted optical waveguides 42b and 42c in their extending direction ranges from 10 to 30 mm. The central portions of the phase-shifted optical waveguides 42b and 42c are separated by a given interval in the width direction and extend parallel to each other. The interval between the central portions of the phase-shifted optical waveguides 42b and 42c ranges from 15 to 50 μm. It should be noted that there are no particular restrictions on the width W of the input / output optical waveguides 42a, the length of the phase-shifted optical waveguides 42b and 42c, and the interval between the phase-shifted optical waveguides 42b and 42c; their dimensions can be arbitrarily set.

[0052] The buffer layer 43 is provided to prevent a portion of the light propagating along the optical waveguide 42 from being absorbed by the modulation electrode section 44. The buffer layer 43 is mainly made of silicon dioxide (SiO2) film or the like, and its thickness is about 0.1 to 1.0 μm.

[0053] In the optical modulator 1, the modulation electrode section 44 is composed of a segmented electrode, which consists of three electrodes 46, 47, and 48 that are segmented along the length of the branch interference type optical waveguide 42 and capacitively coupled to each other. It should be noted that electrode 46 is part of the modulation electrode 11, and electrode 48 is part of the modulation electrode 12. Electrode 46, which is part of the modulation electrode 11 on the signal input side, has an electrode section 46a disposed between phase-shifted optical waveguides 42b and 42c. Electrode 47 has an electrode section 47b disposed on both sides of electrode section 46a, sandwiching phase-shifted optical waveguides 42b and 42c, and an electrode section 47a disposed between phase-shifted optical waveguides 42b and 42c. Electrode 48, which is part of the modulation electrode 12, has an electrode section 48b disposed on both sides of electrode section 47a, sandwiching phase-shifted optical waveguides 42b and 42c. Between modulation electrodes 11 and 12, electrodes 46 and 47, and electrodes 47 and 48 are connected in series with mutual capacitive coupling.

[0054] The light incident and exit ends of the input / output optical waveguide 42a of the substrate 41 are coupled to the incident and exit end faces of the input / output optical fiber 2. The light reflecting section 45 reflects the light incident from the input / output optical waveguide 42a and propagating along the phase-shifted optical waveguides 42b and 42c, causing it to return from the phase-shifted optical waveguides 42b and 42c to the input / output optical waveguide 42a for propagation. By applying a voltage between the modulation electrodes 11 and 12, mutually opposing electric fields are applied to the two phase-shifted optical waveguides 42b and 42c between electrode sections 46a and 47b and between electrode sections 47a and 48b. Accordingly, mutually opposing refractive index changes are generated in the phase-shifted optical waveguides 42b and 42c, and the light passing through them generates phase shifts of opposite polarities. When these lights converge, they interfere with each other, resulting in intensity changes. Accordingly, an optical intensity modulation signal with an intensity change corresponding to the voltage applied between the modulation electrodes 11 and 12 can be obtained.

[0055] Figure 4 This is a schematic diagram illustrating one example of the electromagnetic shielding effect measurement results of the package 8 of the photovoltage probe in this embodiment. The output signal strength originating from the output terminal 26 was measured by rotating the package 8 around its length axis, causing a 360-degree change in the incident direction of the electromagnetic wave, with the contact terminal mounting portion exposed to an electromagnetic wave of the measurement frequency. The measurement results are given in a circular bar graph. The center represents an output strength value of -100 dBm, and the outermost ring represents -50 dBm. The dashed line indicates the measurement value 35, which is the measurement value when the optical modulator 1, the same as that of the photovoltage probe 10 in Embodiment 1, is built into a resin package of the same shape as the package 8. The solid line indicates the measurement value 36, which is the measurement value of the photovoltage probe 10 of this embodiment using the package 8. This embodiment shows that, regardless of the orientation, even compared to using a resin package, which is considered to produce some attenuation compared to the case without a package, an attenuation of 15 dB or more is obtained. This confirms that the package 8 provides sufficient shielding.

[0056] Example 2

[0057] Figure 5 This is a schematic diagram of the photovoltage probe structure according to Embodiment 2, wherein... Figure 5 (a) is a top view with perspective. Figure 5 (b) is a partially enlarged sectional view showing the cross-sectional structure of the package. For example... Figure 5 As shown, in the photovoltage probe 30 of this embodiment 2, the optical modulator 1, the same as in embodiment 1, is fixed inside the package 31. The photovoltage probe 30 is identical in structure to the photovoltage probe 10 of embodiment 1, except for the package 31. In this embodiment, to reduce electromagnetic wave reflection caused by the package 31, the package 31 is constructed by providing a thin sheet-like electromagnetic wave absorber 33 on the surface of a metal package 32.

[0058] Here, the metal package 32 is made of the same material and shape as the package 8 in Embodiment 1. The electromagnetic wave absorber 33 is a sheet made of an inductive electromagnetic wave absorbing material that is mixed with dielectrics such as carbon powder and rubber, polyurethane foam, and polystyrene foam to increase the inductive loss on the surface. It is pasted on the entire surface of the metal package 32 except for the exposed surfaces of the contact terminal mounting parts 5 and 6 and the fixing parts 13 of the input and output optical fibers 2.

[0059] In this embodiment, the electromagnetic wave noise reflected from the package 31 placed near the measurement point is reduced by the electromagnetic wave absorber 33, which prevents noise from mixing into the measured circuit and further reduces the influence of electromagnetic wave noise during measurement. In addition, since it can be constructed simply by pasting the electromagnetic wave absorber sheet onto the surface, the manufacturing process can be simplified.

[0060] Example 3

[0061] Figure 6 This is a schematic diagram of the photovoltage probe according to Embodiment 3, wherein... Figure 6 (a) is a top view with perspective. Figure 6 (b) is a partially enlarged sectional view showing the cross-sectional structure of the package. For example... Figure 6 As shown, in the photovoltage probe 50 of this embodiment, the optical modulator 1, the same as in embodiment 1, is fixed inside the encapsulation 51. The photovoltage probe 50 is identical in structure to the photovoltage probe 10 of embodiment 1, except for the encapsulation 51. In this embodiment, the encapsulation 51 is constructed as follows: a metal sheet 53 is adhered to the surface of a resin encapsulation 52, and then a sheet-like radio wave absorber 54, made of the same material as the radio wave absorber 33 in embodiment 2, is adhered to it.

[0062] Here, the resin encapsulation 52 is constructed with the same shape as the encapsulation 8 in Embodiment 1, and the metal sheet 53 is, for example, a copper adhesive tape. The metal sheet 53 and the radio wave absorber 54 are adhered to the entire surface of the resin encapsulation 52, except for the exposed surfaces of the contact terminal mounting portions 5 and 6 and the fixing component 13 of the input / output optical fiber 2. It should be noted that in this embodiment, the contact terminal mounting portions 5 and 6 are fixed to the resin encapsulation 52.

[0063] Similar to Embodiment 2, this embodiment, while effectively shielding electromagnetic noise, reduces the reflection of electromagnetic noise originating from the encapsulation 51, thereby minimizing the impact of electromagnetic noise on the measured circuit. Furthermore, in this embodiment, since resin is used as the main material for the encapsulation, it enables the light weight and low cost of the photovoltage probe.

[0064] Example 4

[0065] Figure 7 This is a schematic representation of the photovoltage probe structure according to Embodiment 4, shown as a transmittance top view. Figure 7 As shown, in the photovoltage probe 60 of this embodiment, the optical modulator 1, the same as in embodiment 1, is fixed inside the package 61. Compared to the photovoltage probe 10 of embodiment 1, the photovoltage probe 60 has the same structure except for the package 61. In this embodiment, the package 61 is constructed using an electromagnetic wave absorber.

[0066] Here, the package 61, except for its thickness, has the same shape as the package 8 in Embodiment 1, and the contact terminal mounting portions 5 and 6 are fixed to the package 61. The material of the package 61, i.e., the electromagnetic wave absorber, can be a magnetic electromagnetic wave absorbing material such as pure iron. Conductive electromagnetic wave absorbing materials or inductive electromagnetic wave absorbing materials can also be used, provided that the necessary strength can be obtained. In addition, two or more electromagnetic wave absorbing material layers can be stacked and combined. For example, an electromagnetic wave absorbing material of the same type as in Embodiments 2 and 3 can be provided on the surface of the package of magnetic electromagnetic wave absorbing material.

[0067] This embodiment, like embodiment 2, can reduce the reflection of electromagnetic noise originating from the package 61 while effectively shielding electromagnetic noise.

[0068] As described above, according to the present invention, a photoelectric voltage probe can be obtained that can accurately measure the voltage signal of the measured point without being affected by surrounding electromagnetic noise. In particular, devices controlled by high-power signals, such as the drive circuit or control circuit of an automobile, often generate significant electromagnetic noise, the impact of which cannot be ignored. When measuring, for example, the drive circuit or control circuit of an automobile, using the aforementioned photoelectric voltage probe, the voltage signal waveform between the two points constituting the measured object can be accurately measured. Furthermore, even circuit boards located near the drive circuit or control circuit of an automobile can be accurately measured, allowing for the accurate measurement of the voltage signal waveform between the two points constituting the measured object. Additionally, sometimes the voltage signal waveform between the two points constituting the measured object can be accurately measured near the drive circuit or control circuit of an automobile, enabling noise measurement at that location.

[0069] Needless to say, the present invention is not limited to the above embodiments and can be modified in various ways according to the purpose. For example, the type of optical modulator used is not limited to reflective type, but can also be a transmissive type optical modulator. Furthermore, when the modulation electrode is a segmented electrode, the number of segments can be arbitrarily set according to the frequency, amplitude, etc. of the target measured voltage. The modulation electrode may not be a segmented electrode. The shape, structure, connection, and fixing method of the contact terminal and the contact terminal mounting part can be selected according to the purpose. In addition, the material of the package can also be selected according to the shielding performance and reflection performance of the target radio wave. The shape or structure of the package can also be arbitrarily selected. For example, in addition to the cube shape in the above embodiments, it can also be a cylindrical shape or the like.

Claims

1. A photoelectric voltage probe comprising an optical modulator, an input optical fiber and an output optical fiber connected to the optical modulator, two contact terminals or a mounting portion for the two contact terminals, and a package housing the optical modulator, the input optical fiber, and a portion thereof; the optical modulator having at least two modulation electrodes, and outputting light by intensity modulation of incident light depending on the voltage between the two modulation electrodes; the two contact terminals being connected to the modulation electrodes and capable of contacting a point to be measured; the mounting portion for the two contact terminals having a structure for detachably contacting the contact terminal connected to the modulation electrodes and capable of contacting the point to be measured; wherein the voltage signal induced between the two modulation electrodes by the contact terminals is converted into a light intensity modulation signal by the optical modulator and output from the output optical fiber; characterized in that, The aforementioned package has a structure in which the interior is covered by a layered or sheet-like metal body, and has the following electromagnetic shielding effect: when the aforementioned contact terminal or the aforementioned contact terminal mounting portion is opened and irradiated with an electromagnetic wave of the measurement frequency, the output signal strength is attenuated by more than 15 dB compared to when the package is not present; the interval between the aforementioned two contact terminals or the interval between the aforementioned two contact terminal mounting portions is more than 3 mm, wherein the aforementioned contact terminal mounting portion is composed of a cylindrical insulator and a cylindrical terminal insertion portion of metal fixed therein, and the aforementioned contact terminal is used to insert into the terminal insertion portion of the contact terminal mounting portion.

2. A photoelectric voltage probe comprising an optical modulator, an input optical fiber and an output optical fiber connected to the optical modulator, two contact terminal mounting portions, and a package housing a portion of the optical modulator, the input optical fiber, and the output optical fiber; the optical modulator having at least two modulation electrodes, and outputting light by intensity modulation based on the voltage between the two modulation electrodes; the two contact terminal mounting portions having a structure for detachably connecting to the modulation electrodes and contacting a contact terminal that can contact a point to be measured; the contact terminal mounting portions being located further inward than the surface of the package; wherein the voltage signal induced between the two modulation electrodes by the contact terminal is converted into a light intensity modulation signal by the optical modulator and output from the output optical fiber; characterized in that... The aforementioned package has the following electromagnetic shielding effect: when the aforementioned contact terminal mounting portion is opened and irradiated with electromagnetic waves of the measurement frequency, the output signal strength is attenuated by more than 15 dB compared to when the package is not present; the distance between the aforementioned two contact terminal mounting portions is more than 3 mm, wherein the aforementioned contact terminal mounting portion is composed of a cylindrical insulator and a cylindrical terminal insertion portion of metal fixed inside therein, and the aforementioned contact terminal is used to insert into the terminal insertion portion of the contact terminal mounting portion.

3. A photoelectric voltage probe comprising an optical modulator, an input optical fiber and an output optical fiber connected to the optical modulator, two contact terminals or a mounting portion for the two contact terminals, and a package housing a portion of the optical modulator, the input optical fiber, and the output optical fiber; the optical modulator having at least two modulation electrodes, and outputting light by intensity modulation of incident light based on the voltage between the two modulation electrodes; the two contact terminals being connected to the modulation electrodes and capable of contacting a point to be measured; the mounting portion for the two contact terminals having a structure for detachably contacting the contact terminal connected to the modulation electrodes and capable of contacting the point to be measured; wherein the voltage signal induced between the two modulation electrodes by the contact terminals is converted into a light intensity modulation signal by the optical modulator and output from the output optical fiber; characterized in that... The aforementioned package has an electromagnetic wave absorber for reducing the reflection of electromagnetic waves arriving from outside the package caused by the package; the aforementioned package has an electromagnetic wave shielding effect such that when the aforementioned contact terminal or the aforementioned contact terminal mounting portion is opened and irradiated with electromagnetic waves of a measured frequency, the output signal strength is attenuated by more than 15 dB compared to when the package is not present; the interval between the aforementioned two contact terminals or the interval between the aforementioned two contact terminal mounting portions is 3 mm or more, wherein the aforementioned contact terminal mounting portion is composed of a cylindrical insulator and a cylindrical terminal insertion portion of metal fixed therein, and the aforementioned contact terminal is used to insert into the terminal insertion portion of the contact terminal mounting portion.

4. The photovoltage probe according to claim 3, characterized in that, The aforementioned electromagnetic wave absorber is a thin sheet-like electromagnetic wave absorber present on the surface of the aforementioned package.

5. The photovoltage probe according to claim 3 or 4, characterized in that, The aforementioned packaged component achieves the aforementioned electromagnetic shielding effect by reducing electromagnetic wave transmission through the aforementioned electromagnetic wave absorber.

6. The photovoltage probe according to any one of claims 1 to 5, characterized in that, The aforementioned optical modulator is a branch-interference type optical modulator that employs an optical waveguide formed on a lithium niobate crystal substrate.

7. The photovoltage probe according to claim 6, characterized in that, The aforementioned optical modulator is a reflective optical modulator that internally reflects incident light to refract it back, and the aforementioned input optical fiber and output optical fiber are composed of a single input and output optical fiber.

8. The photovoltage probe according to claim 6 or 7, characterized in that, At least one of the two modulation electrodes is capacitively coupled to the two modulation electrodes.

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